Adaptive transmission feedback

Abstract

A method, program and apparatus for transmitting from a transmitter to a receiver over a channel using a transmit diversity scheme. The method comprises: receiving power-related information fed back from the receiver to the transmitter; and at the transmitter, using the power-related information to generate channel state information. The method further comprises using the generated channel state information to control for subsequent transmission to the receiver from the multiple transmit antennas of the transmitter.

The invention claimed is: 
     
       1. A method of transmitting from a transmitter to a receiver over a channel using a transmit diversity scheme whereby data transmitted from one of multiple transmit antennas of the transmitter is the same as data transmitted from others of the multiple transmit antennas, the same data being transmitted with different relative weightings, the method comprising:
 for each of a plurality of time intervals, receiving power-related information fed back from the receiver to the transmitter, relating to a combined power from the multiple antennas as received at the receiver over said channel, wherein the power-related information is fed back for a primary purpose other than transmit diversity to control a function of the transmitter relating to the primary purpose, the primary purpose comprises at least one of:
 controlling the combined power of the channel, and 
 adaptive modulation; 
 
 at the transmitter, applying a recursive filter to generate channel state information relating to the transmit diversity of the channel for each of said plurality of time intervals, wherein the application of the recursive filter comprises estimating the channel state information for a current time interval based on the estimated channel state information from a previous time interval, and refining the estimated channel state information for the current time interval using the power-related information for the current time interval; and 
 using the generated channel state information to control the relative weightings for subsequent transmission to the receiver from the multiple transmit antennas of the transmitter. 
 
     
     
       2. The method of  claim 1 , wherein the application of said filter comprises applying a Kalman filter algorithm. 
     
     
       3. The method according to  claim 1 , wherein said generation is performed without receiving explicit channel state information fed back from the receiver indicating the receiver's preferred weightings, by instead using said power-related information to generate said channel state information at the transmitter. 
     
     
       4. The method according to  claim 1 , wherein the power-related information comprises a measure of received signal power relative to disturbance. 
     
     
       5. The method according to  claim 4 , wherein said measure comprises a ratio of signal power to interference-plus-noise. 
     
     
       6. The method according to  claim 4 , wherein said measure comprises a channel quality indicator. 
     
     
       7. The method according to  claim 4 , wherein said measure comprises at least one of an SNR and a CQI of a 3 GPP standard. 
     
     
       8. The method according to  claim 1 , wherein the power-related information comprises a power control command. 
     
     
       9. The method according to  claim 8 , wherein the power control command comprises a TPC command of a 3GPP standard. 
     
     
       10. The method of  claim 8 , wherein said refinement of the estimated channel state information for the current time interval is performed using a measurement based on: the power control command for the current time interval, and a step value by which the combined power from the transmitter is raised or lowered in response to a power control command. 
     
     
       11. The method according to  claim 1 , wherein the power-related information comprises an acknowledgment message or non-acknowledgment message relating to previous transmitted data. 
     
     
       12. The method according to  claim 11 , comprising applying a different degree of relative bias to one of the acknowledgment and non-acknowledgement before use in said recursive filter. 
     
     
       13. The method according to  claim 12 , comprising dynamically adjusting said degree of relative bias to maximise a long term performance metric. 
     
     
       14. The method according to  claim 1 , wherein the different relative weightings define at least different relative phases, and said use of the generated channel state information to control the relative weightings comprises controlling the relative phases. 
     
     
       15. The method according to  claim 1 , wherein the different relative weightings define different amplitudes, and said use of the generated channel state information to control the relative weightings comprises controlling the relative amplitudes. 
     
     
       16. The method according to  claim 1 , wherein the method further comprises using the power-related information to determine a reliability measure for the generated channel state information, and also using the reliability measure to control the weightings for a subsequent transmission to the receiver from the multiple transmit antennas of the transmitter. 
     
     
       17. The method according to  claim 1 , wherein said use of the channel state information to control the weightings comprises updating said weightings at a rate of once per period, wherein said period spans a plurality of said time intervals, and said refinement is performed by combining the power-related information received over some or all of the time intervals spanned by said period. 
     
     
       18. The method of  claim 17 , comprising dynamically adjusting said period in order to maximise a long term performance metric. 
     
     
       19. The method according to  claim 13 , wherein the long-term performance metric comprises at least one of: average power saving and average link capacity. 
     
     
       20. The method according to  claim 1 , comprising regularising said weightings so as to ensure at least a minimum degree of diversity of directions in transmission to the receiver. 
     
     
       21. The method according to  claim 1 , comprising operating the transmitter in at least two different modes of operation at different times:
 a first mode of operation in which the same data is transmitted from multiple transmit antennas of the transmitter with different relative weightings; and 
 a second mode of operation in which data is transmitted from only a selected one or more of the multiple transmit antennas, by applying a non-zero weighting to only the selected one or more transmit antennas; 
 wherein in both modes, the weightings are controlled using the generated channel state information. 
 
     
     
       22. The method of  claim 21 , wherein in the second mode of operation the data is transmitted from only a selected one of the multiple transmit antennas. 
     
     
       23. The method of  claim 1 , wherein said refinement of the estimated channel state information for the current time interval is performed using a combined measurement based on the power-related information over a period spanning multiple time intervals. 
     
     
       24. The method of  claim 23 , wherein the combined measurement comprises an average measurement based on the power-related information for the multiple time intervals. 
     
     
       25. A transmitter comprising:
 multiple transmit antennas; 
 transmission circuitry coupled to the multiple transmit antennas, arranged to transmit to a receiver over a channel using a transmit diversity scheme whereby data transmitted from one of the multiple transmit antennas is the same as data transmitted from others of the multiple transmit antennas, the same data being transmitted with different relative weightings; 
 reception circuitry arranged to receive, for each of a plurality of time intervals, power-related information fed back from the receiver to the transmitter, relating to a combined power from the multiple antennas as received at the receiver over said channel, wherein the power-related information is fed back for a primary purpose other than transmit diversity to control a function of the transmitter relating to the primary purpose, the primary purpose comprises at least one of:
 controlling the combined power of the channel, and 
 adaptive modulation; and 
 
 signal processing apparatus coupled to the transmission and reception circuitry, and configured to apply a recursive filter to generate channel state information relating to the transmit diversity of the channel for each of said plurality of time intervals, wherein the application of the recursive filter comprises estimating the channel state information for a current time interval based on the estimated channel state information from a previous time interval, and refining the estimated channel state information for the current time interval using the power-related information for the current time interval; 
 wherein the signal processing apparatus is configured to use the generated channel state information to control the relative weightings for subsequent transmission to the receiver from the multiple transmit antennas of the transmitter. 
 
     
     
       26. The transmitter according to  claim 25 , wherein the signal processing apparatus is configured a Kalman filter as the recursive filter. 
     
     
       27. A program product for transmitting from a transmitter to a receiver over a channel using a transmit diversity scheme whereby data transmitted from one of multiple transmit antennas of the transmitter is the same as data transmitted from others of the multiple transmit antennas, the same data being transmitted with different relative weightings, the program product comprising code embodied on a non-transitory computer-readable medium and configured so as when executed on a processor to:
 for each of a plurality of time intervals, receive power-related information fed back from the receiver to the transmitter, relating to a combined power from the multiple antennas as received at the receiver over said channel, wherein the power-related information is fed back for a primary purpose other than transmit diversity to control a function of the transmitter relating to the primary purpose, the primary purpose comprises at least one of:
 controlling the combined power of the channel, and 
 adaptive modulation; 
 
 at the transmitter, apply a recursive filter to generate channel state information relating to the transmit diversity of the channel for each of said plurality of time intervals, wherein the application of the recursive filter comprises estimating the channel state information for a current time interval based on the estimated channel state information from a previous time interval, and refining the estimated channel state information for the current time interval using the power-related information for the current time interval; and 
 use the generated channel state information to control the relative weightings for subsequent transmission to the receiver from the multiple transmit antennas of the transmitter. 
 
     
     
       28. The program product of  claim 27 , wherein the recursive filter is a Kalman filter. 
     
     
       29. A method of transmitting from a transmitter to a receiver over a channel using a transmit diversity scheme whereby data can be transmitted from a selected one or more of multiple transmit antennas of the transmitter, the method comprising:
 at the transmitter, for each of a plurality of time intervals, receiving power-related information fed back from the receiver to the transmitter, relating to a power from the one or more selected transmit antennas as received at the receiver over said channel, wherein the power-related information is fed back for a primary purpose other than transmit diversity to control a function of the transmitter relating to the primary purpose, the primary purpose comprises at least one of:
 controlling the combined power of the channel, and 
 adaptive modulation; 
 
 at the transmitter, applying a recursive filter to generate channel state information relating to the transmit-diversity of the channel for each of said plurality of time intervals, wherein the application of the recursive filter comprises estimating the channel state information for a current time interval based on the estimated channel state information from a previous time interval, and refining the estimated channel state information for the current time interval using the power related information for the current time interval; and 
 using the generated channel-related information to select which of the multiple transmit antennas to use for subsequent transmission to the receiver. 
 
     
     
       30. The method of  claim 29 , whereby said data is transmitted from only a selected one of the multiple transmit antennas at any one time. 
     
     
       31. The method of  claim 29 , wherein said power-related information comprises a power control command. 
     
     
       32. The method of  claim 31 , wherein said refinement of the estimated channel state information for the current time interval is performed using a measurement based on: the power control command for the current time interval, and a step value by which the power from the one or more selected transmit antennas is raised or lowered in response to a power control command. 
     
     
       33. The method of  claim 29 , wherein said refinement of the estimated channel state information for the current time interval is performed using a combined measurement based on the power-related information over a period spanning multiple time intervals. 
     
     
       34. The method of  claim 33 , wherein said combined measurement comprises an average measurement based on the power-related information for the multiple time intervals. 
     
     
       35. A transmitter comprising:
 multiple transmit antennas; 
 transmission circuitry coupled to the multiple transmit antennas, arranged to transmit to a receiver over a channel using a transmit diversity scheme whereby data can be transmitted from a selected one or more of the multiple transmit antenna; 
 reception circuitry arranged to receive for each of a plurality of time intervals power-related information fed back from the receiver to the transmitter, relating to a power from the one or more selected transmit antennas as received at the receiver over said channel, wherein the power-related information is fed back for a primary purpose other than transmit diversity to control a function of the transmitter relating to the primary purpose, the primary purpose comprises at least one of:
 controlling the combined power of the channel, and 
 adaptive modulation; and 
 
 signal processing apparatus coupled to the transmission and reception circuitry, configured to apply a recursive filter to generate channel state information relating to the transmit-diversity of the channel for each of said plurality of time intervals, wherein the application of the recursive filter comprises estimating the channel state information for a current time interval based on the estimated channel state information from a previous time interval, and refining the estimated channel state information for the current time interval using the power related information for the current time interval; 
 wherein the signal processing apparatus is further configured to use the generated channel-related information to select which of the multiple transmit antennas to use for subsequent transmission to the receiver. 
 
     
     
       36. The transmitter according to  claim 35 , whereby data is transmitted from only a selected one of the multiple transmit antennas at any one time. 
     
     
       37. A program product for transmitting from a transmitter to a receiver over a channel using a transmit diversity scheme whereby data can be transmitted from a selected one or more of multiple transmit antennas of the transmitter, the program product comprising code embodied on a non-transitory computer-readable medium and configured so as when executed on a processor to:
 for each of a plurality of time intervals, receive power-related information fed back from the receiver to the transmitter, relating to a power from the one or more selected transmit antennas as received at the receiver over said channel, wherein the power-related information is fed back for a primary purpose other than transmit diversity to control a function of the transmitter relating to the primary purpose, the primary purpose comprises at least one of:
 controlling the combined power of the channel, and 
 adaptive modulation; 
 
 applying a recursive filter to generate channel state information relating to the transmit-diversity of the channel for each of said plurality of time intervals, wherein the application of the recursive filter comprises estimating the channel state information for a current time interval based on the estimated channel state information from a previous time interval, and refining the estimated channel state information for the current time interval using the power related information for the current time interval; and 
 use the generated channel-related information to select which of the multiple transmit antennas to use for subsequent transmission to the receiver. 
 
     
     
       38. The program product of  claim 37 , whereby data is transmitted from only a selected one of the multiple transmit antennas at any one time.